Make langchain-openai and langchain-anthropic optional dependencies

[ystarikovich]

Problem

langchain-openai and langchain-anthropic are currently listed as required dependencies in pyproject.toml, but neither is directly imported in any executable source code. They are only resolved at runtime by langchain.chat_models.init_chat_model() when a user explicitly requests a specific LLM provider via a string identifier (e.g. "openai:gpt-4o" or "anthropic:claude-3-5-sonnet-latest").

This means installing langmem pulls in both provider SDKs (and their transitive dependencies like openai, anthropic, tiktoken, etc.) even when:

• A user only needs one provider
• A user passes a pre-instantiated model object and doesn't need either provider SDK — the init_chat_model() factory is never invoked in this case, making both packages completely unused

Evidence

Dependency	Required?	Actual usage in source
langchain-openai>=0.3.1	Hard required	Only referenced in docstring examples (short_term/summarization.py). Never imported in executable code.
langchain-anthropic>=0.3.3	Hard required	Never directly imported. Only loaded dynamically by init_chat_model() at runtime when a user passes an Anthropic model string.
langchain-core	Hard required	Legitimately required — 56+ top-level imports across the codebase
langchain	Hard required	Legitimately required — init_chat_model imported in 3 modules
langgraph	Hard required	Legitimately required — 20+ top-level imports
langsmith	Hard required	Legitimately required — top-level imports in 5 modules
trustcall	Hard required	Legitimately required — top-level imports in 4 modules

Proposal

Move langchain-openai and langchain-anthropic to optional dependency groups:

[project.optional-dependencies]
openai = ["langchain-openai>=0.3.1"]
anthropic = ["langchain-anthropic>=0.3.3"]
all = [
    "langchain-openai>=0.3.1",
    "langchain-anthropic>=0.3.3",
]

Users would install only what they need:

pip install langmem                # Core only — works with pre-instantiated models
pip install langmem[openai]        # OpenAI provider
pip install langmem[anthropic]     # Anthropic provider
pip install langmem[all]           # Both providers

Impact

• No breaking changes to code — init_chat_model() already handles missing providers with a clear error message at runtime
• Lighter default install — removes openai, anthropic, tiktoken, httpx, and other transitive deps for users who don't need them
• Better developer experience — users who pass custom model instances don't have to install unused SDKs

P.S.

Want to validate the general vision of the team on this. Happy to submit the PR